Total chemical synthesis, characterization, and immunological properties of an MHC class I model using the TASP concept for protein de novo design

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Abstract
The design, total chemical synthesis, and immunological properties of a four‐α‐helix bundle template‐assembled synthetic protein (TASP) mimicking some of the structural features of the major histocompatibility complex (MHC) class I is described. In a first approach, the native sequence 58–74 of the α1 heavy chain domain of HLA‐A2 was modeled in order to increase helix stability and amphiphilicity of the 17‐mer peptide, preserving the residues for potential T‐cell receptor (TcR) binding properties. According to the TASP concept, these helical segments were covalently attached to a cyclic template molecule designed for the induction of a four‐helix‐bundle topology of the assembled peptide blocks.After extensive HPLC purification, stepwise solid‐phase synthesis resulted in a TASP molecule of high chemical purity as demonstrated by analytical HPLC, mass spectrometry, and amino acid analysis. CD spectroscopic investigations are consistent with the onset of a partial α‐helical conformation in aqueous buffer as well as in TFE. Antibodies raised directly against this four‐α‐helix bundle TASP molecule (without prior conjugation to a carrier molecule) were detected by ELISA. Flow cytometry studies showed that these antibodies recognize the native MHC class I molecule on the surface of HLA‐A2‐positive cells. The results indicate that the TASP approach represents a versatile tool for mimicking conformational epitopes.